CHARACTERIZATION OF TARS FROM VARIABLE HEATING RATE PYROLYSIS OF MACERAL CONCENTRATES

Product yields and structures of tars from the pyrolysis of a set of maceral concentrates derived from Linby coal were determined and compared as a function of heating rate (1 and 1000 K s-1) and temperature (400-900-degrees-C). A new trap was developed for the collection and quantitative recovery of tars evolved during atmospheric pressure wire-mesh pyrolysis experiments, allowing the capture and recovery of tars expected to reflect closely the characteristics of evolved primary tars. Yields from all three maceral concentrates were found to increase with increasing heating rate, but the liptinite concentrate showed the smallest sensitivity. Tar characterization was undertaken with size exclusion chromatography and u.v. fluorescence spectroscopy. Comparison of molecular mass distributions suggested that liptinite concentrate tars contain greater fractions of large molecular mass units than corresponding vitrinite and inertinite concentrate tars. Molecular mass distributions of liptinite concentrate tars from experiments at 400 and 500-degrees-C, obtained using an evaporative analyser as mass detector. showed the presence of substantial quantities of material not detected by a u.v. detector, set at 254 nm and used in tandem, suggesting that the material identified in this region is predominantly aliphatic/hydroaromatic in character. In fast heating experiments (1000 K s-1), this material tended to diminish rapidly with increasing pyrolysis temperature from 400-500-degrees-C to 600-900-degrees-C, suggesting intraparticle destruction. Results from u.v. fluorescence spectroscopy suggest the presence of substantially similar aromatic cluster size distributions in vitrinite and liptinite tars; greater intensities of spectra from vitrinite concentrate tars suggest, however, the presence of greater concentrations of aromatic clusters and/or polars within vitrinite tars.